Two words:
Intel i810
That and some "all in one" inregrated solutions from via that lacked agp are reason why people would still want/need the PCI variant, and why they still make them. Outside of an old dual monitor deal, which is easier to achieve now just by buying one good agp card instead of agp+pci, it's like the only reason they manufacturer PCI nvidia cards.
You have a lot of decent speed celeron pcs out there, using some lame 8 meg intel integrated graphics. While they will never become top gaming rigs, for many people being able to run something as mundane as a RTS game is a step up and a PCI card like this is their only salvation.